The NV4500 is a 5-speed constant mesh manual transmission. All gear
ranges including reverse are synchronized. The transmission is a top loader
design with a cast iron gear case and an aluminum shift cover.
Two versions of the NV4500 are used in
1994+ models. A standard duty version is used for 5.2L and 5.9L applications
and a heavy duty version is used for V10, and Cummins diesel engines. The main
differences between the two versions concern the larger input and output shafts
used in the heavy duty version.
The NV4500 is a top loader style transmission.
The shift lever is located in the shift cover bolted to the top of the shift
cover and operates the shift forks and rails directly. The shift forks and rails
are all located within the aluminum cover which is bolted to the top of the
gear case.
Dual cone synchronizers are used for
first and second gears, similar to the T5 design. The 1-2 synchronizer also
has a set of spring loaded flyweights in the synchro hub that govern shift speeds,
to prevent over-revving the motor on a 2-1 downshift.
A reverse gear inhibitor mechanism
prevents reverse gear engagement when shifting into forward gear ranges. The
inhibitor mechanism is located in the shift cover.
Tapered roller bearings support the drive
gear, mainshaft, and countershaft in the gear case. Pilot roller bearings in
the drive gear hub support the forward end of the mainshaft. The mainshaft gears
are all supported on caged type roller bearings. Drive gear thrust reaction
is controlled by a needle type thrust bearing located at the forward end of
the mainshaft.
An identification tag is attached to the
driver side PTO cover. Yhis tag provides the transmission model number, build
date, and part number. Do not lose this tag, the information it contains is
essential for correct parts ordering!
The reverse gear and forward gears 1-4 are
mounted inside the main transmission case. 5th gear is mounted in the tailshaft
assembly.

*Around the 1998 model year, the reverse gear ratio was changed from
5.61 to 5.04. The pre-98 reverse gear on the main shaft has a diameter of 6-5/8"
with 39 teeth; the later gear has a diameter of 6" with 35 teeth.

The 450 Lb-ft input rating is a continuous and conservative
input rating for a long transmission life. The transmission can easily withstand
higher torque from diesels with aftermarket power kits, but transmission life
will be reduced in proportionately. Keep in mind that 5th gear has failed on
some trucks that regularly pull or haul heavy loads. If you wish to avoid 5th
gear failure, do not mash the throttle with the engine turning less than 1600
rpm while in 5th gear.
Note: The 24 Valve diesel engine
has a rated torque peak of 460 lb-ft. Either the engine specs lie, or the transmission
can take more than 450 lb-ft, despite its rating.

Using helical gearing with all speed gears in constant
mesh and all speeds synchronized, this transmission will handle 450 ft-lbs of
torque, and vehicles with a combined gross weight of 19,000 pounds. The 4500
uses a dual cone synchronizer for first and second gears, similar to the familiar,
world class T5 design. The 1-2 synchronizer also has a set of spring loaded
flyweights in the synchro hub that govern shift speeds, to prevent over-revving
the motor on a 2-1 downshift. (from Gears Magazine March 1998)

Other Lube Oils for
the NV4500

Joe Donnelly tested several brands of oil for the NV4500 and reported the results
in TDR issue #??. He also posted tothe TDR Roundtable "The Castrol was
best, flat out. Torco RTF was very close, and has the GL6 additive rating for
those worried about gear wear. If the lube doesn't get hot, it is easier on
the brass synchros. The Castrol and Torco were slow to heat up. It took several
full power passes on the dyno to get them to 140 deg. Another popular lube came
up to temperature with just one pass. That suggests to me that friction was
higher with it, and its higher drag figures (taken in neutral gear, coasting
down from 110 mph) supported that guess. However, to get another kind of answer
I asked the possibly most learned pertroleum/lubricant engineer (degrees, certifications,
etc.), Kevin Dinwiddie. He told me to use Castrol. He sells LE and could have
recommended their LE607 (90 wt) or LE606 (80 wt?). Since he took his company
out of the controversy, and therefore "doesn't have a dog in this fight" I felt
his advice was well meant, and not self serving in any way."

The NV-4500 calls for an GL-4 oil. A GL-4 oil has about 1/2 the sulfur/phoshphorus
anti wear additive as a GL-5 does. The LE 607 is a GL-5. NV Gear is asking for
a lesser amount of sulfur/phoshphorus becasue of the possibility of the sulfur
attacking the light metals in the transmission. Because yellow metals are primarily
attacked at high temperatures, systhetic GL-5 oils may not pose a problem due
to their lower operating temperatures. Many are using synthetic alternatives
to the recommended Castrol oil, whether or not you should is a decision that
you should based on your own research.

RedLine MT-90 GL-4 75-90 - recommended by some TDR members who claim
it works well.

LE 607 SAE 90 has been used in this application for many years with
no problems at all because of the buffer package that they use in the 607 product.
It basicly keeps the sulfer in check and does not have an effect on the light
metals. This is a quote from the back of the Technical Data Bulletin of the
607 "Use in differentials and transmissons (except those requiring non-ep pur
mineral oil) in over-the-road and stop-n-go fleets and off highway equipment.
Use in all heavily-loaded industrial enclosed gears. Especially appropriate
for heavy donstruction equipment and farm machinery where service is severe.
Should be used where drain periods may be longer than normal due to equipment
being away from home terminals or difficult access. For use in worm gearboxes
and in gearboxes that have bronze gears and thrust washers which require extreme
pressure gear oil. Especially appropriate for bowl mills, pellet mills, rock
and coal crushers, machine tool gearboxes, gear heads, soy bean oil extractors
and other industrial applications.

Amsoil Series 2000 75W-90 - Many have reported success with with this
oil. A few have reported that shifting was more difficult, most report improvements
in the shifting.